This invention relates to the manufacture of metal dithiophosphates and to the composition manufactured. More specifically this invention relates to a process for the neutralization of dithiophosphoric acids.
It is well known that various additives can be added to lubricating oils in order to improve various oil properties and to make a more satisfactory lubricant. Antiwear agents are intended to decrease wear of machine parts. Wear inhibitors for incorporation in motor oils and industrial oils are finding greater use as a result of greater stress placed on moving parts in high performance engines. Numerous additives have been developed for use in such oil compositions to improve the lubricating characteristics thereof and thereby to lessen the wear of the moving parts.
Metal diaryl or dialkyl dithiophosphates, especially zinc diaryl or dialkyl dithiophosphates (ZOP), have long been used as antiwear additives and antioxidants in hydraulic oils, motor oils and automatic transmission fluids. In the manufacture of such metal dithiophosphates, a dithiophosphoric acid is commonly neutralized with a base, such as zinc oxide or hydroxide. This neutralization step does not take place readily and commonly a large excess of the base is used in conjunction with a neutralization promoter and high neutralization temperatures in order to achieve reasonably short reaction time. Sometimes the use of promoters such as nitric acid can lead to undesirable side effects such as haze problems or instability. In many cases the neutralized product is difficult to filter and has a dark color.
It is an object of this invention to provide an improved process for the manufacture of metal dithiphosphates, especially neutralization of dithiophosphoric acids.
It is an object of this invention to provide an improved process for the continuous neutralization of dithiophosphoric acids requiring shorter neutralization time, a minimum amount of excess metal base, and often requiring no neutralization promoter. Further, this process has a high throughput at minimum capital expenditure. In many cases, highly effective dithiophosphates are made which do not suffer possible detrimental affects of neutralization promoters.